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April 29, 2011

Rebuilding of Christchurch - some interesting articles

Some time ago my son sent me a map of Christchurch showing the swamp land the city has been built on.

Here is a snapshot of part of it... the area I live in. (Click on it to enlarge it). It appears we live on the outer loop of the river between the part marked sand hills and sand... Horse Shoe Lagoon.

The full Canterbury map is available as a pdf file at this link - locals, check out where you live!

Over the weekend, I read about the early 1850's map that showed the branches of our rivers and the tributaries that existed... if these are overlaid over current maps, it helps explains the rather random destruction of buildings in the CBD. Places built on tributaries and old wetlands are more likely to have fallen, sunk, gone. Sadly, people no longer knew what was safe ...

Christchurch’s earthquake-battered central business district (CBD) should not be rebuilt back to what it was before February 22, one of New Zealand’s leading landscape architects Di Lucas said today.

First, city planners and rebuilders need to better respect the natural under-layers to the city, she said.

Lucas reviewed 1850s maps of Christchurch showing wetlands and streams through the city and was little surprised there was so much damage. Liquefaction mapping was predicted, and has occurred on areas with high water table and estuarine sands, and the existing and former natural levees along watercourses have exploded.

`` Fifty percent of buildings in the CBD will likely disappear because of the earthquake. The old maps show some were built above streams apparent at that time. The 1850 mapping suggests the PGG building which collapsed in February was likely built on a levee of silt. The land surface of Christchurch is deceptive, as it was a dynamic plains system,’’ she said.

``About 15 years ago I observed the native forest that had been smashed and buried by Waimakariri floods beneath the Convention Centre site. It reminded me that there is a ‘club sandwich’ of layers of activity under the city. Whilst solid above, old buried layers have liquefied and been extruded by the earthquakes. The land surface has been lowered as a consequence.’’

For those interested, a really good picture explanation about liquefaction around rivers is on this fact sheet and a full copy can be obtained here - this is one part of it.

I realise we have been lucky with this house as although we live across the road that runs along the banks of a river, we appear to have been on the undamaged side. Houses further along on the river edge on the lower side and also, the inner loop in the original swamp area across the river, have seen their houses and streets ravaged. We are one of the original farmhouses for the area so the settlers must have built on firmer land at the time - good luck for us, as believe me, like most of us in Christchurch, the thought of earthquakes was far from my mind when I bought into the house! The wildlife reserve on the river side across our road is mainly closed - it is badly cracked and slipped - in some places there are narrow crevices that would be over our heads if we fell in.

The current City Plan lacks design controls and measures to make the CBD beautiful and sustainable. An urgent change is needed. We don’t want just utilitarian structures. We need a city with the X factor, to attract businesses, workers and visitors. Not again draughty spaces below high-rise and exposed to the easterly; buildings ignoring the solar resource; and, outmoded transport options. We could change it from a tired energy-hungry city to an appealing sustainable garden city.

"This time, we must allow for functioning natural systems; managing rainfall with permeable surfaces; daylighting streams; maximising local materials; greening roofs, and having vegetated public and private spaces forming pleasant micro-climates,’’ said Lucas, a former president of the NZ Institute of Landscape Architects. “Whole street blocks have been mostly destroyed so their layout needs to be re-thought comprehensively to create more appealing urban spaces that showcase cutting-edge design.”

"We need to reorganise spaces and access, with more green areas within a low rise city, using tree canopy – three or four storeys - as a measure. Noosa on the Sunshine Coast formalised their height limits to tree canopy height, and everyone loves that city. You don’t need to see the sea from within the centre, you can sense it, and enjoy the microclimate from a low rise environs.

"It [the map] has the streams on it for the central city, and it's quite a precise layout. It's quite detailed," Lucas said.

When transposed on to the present-day central city, the waterways mirrored some of the areas of worst earthquake damage, she said.

A stream that crossed Manchester St, between Salisbury and Peterborough streets, cut a swath under buildings and the street itself.

"You could plot that line right through all the way," she said.

"There's some very good solid apartments, two or three storeys high, and one block of it has sunk a metre and another block is more or less as it used to be.

"That line continues through the next block and it goes from there and does a drop in Manchester St of a metre."

She said it was "madness" to have intensive building so close to the Avon River on streets such as Fitzgerald Ave.

"They're encroaching and nature has rebelled," Lucas said.

"I think we need to respect the natural systems better."

The new earthquake control system CERA, takes over soon and the national state of emergency can be lifted, some 10 weeks after the quake. Will be interesting to see what happens next...

Meanwhile, I have been thinking of the tornadoes and all the fear for the people in the southern states of America.... another form of random disaster that flattens some areas and not others. The fear and loss will however have an impact on all around them, particularly when so many have been lost in the path of the storms.
Kia Kaha

3 comments:

Hi Fiona, Interesting post - do you (or your son) know where the top map on your post was sourced from? I have posts along similar themes http://envirohistorynz.wordpress.com/2011/05/11/earthquake-reveals-the-forgotten-streams-of-christchurch/ and http://envirohistorynz.wordpress.com/2011/02/26/christchurch-a-city-haunted-by-its-environmental-past/ and would be keen to know its provenance, so that I can refer readers to your post (and map) also. Thanks, envirohistory NZ

Hi - Following back the links it shows the following details - you might be able to find more searching for these as it does not show on the Black Map heritage pages at http://archives.govt.nz/gallery/v/Online%20Regional%20Exhibitions/Chregionalofficegallery/sss/Black%20Map%20of%20Christchurch